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Planetary News: Mercury (2006)

MESSENGER Swings By Venus on its Way to Mercury

Click to enlarge > Venus as seen from MESSENGER This image of Venus was captured by the MESSENGER Dual Imaging System on October 4, 2006, three weeks before MESSENGER's first Venus flyby, from a distance of 16.5 million kilometers (10.3 million miles). It has been enlarged to 400% its original size. It was not possible for MESSENGER to acquire science data from closer distances because Venus was in solar conjunction at the time. Credit: NASA / JHUAPL / CIW

In a maneuver intended to use a planet's gravity to make abrupt changes in a spacecraft's trajectory, NASA's Mercury-bound MESSENGER spacecraft came within 2,990 kilometers (1,860 miles) of the surface of Venus early on Tuesday. The flyby shrunk the radius of MESSENGER'S orbit around the Sun to bring it closer to Mercury.

MESSENGER swung by Venus at 8:34 UTC (4:34 a.m. EDT) on October 24, according to mission operators at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. About 18 minutes after the approach, an anticipated solar eclipse cut off communication between Earth and the spacecraft. Contact was reestablished at 14:15 UTC (10:15 a.m. EDT) through NASA's Deep Space Network, and the team is collecting data to assess MESSENGER's performance during the flyby.

Shortly before the Venus flyby the spacecraft entered superior conjunction, placing it on the exact opposite side of the Sun as Earth, making communication between MESSENGER and Mission Operations difficult, if not impossible. "So we are not making any scientific observations at the time of this flyby," says Carnegie Institution of Washington's Sean C. Solomon, the mission's principal investigator. "We shall conduct a full suite of observations surrounding the second flyby in June 2007.

In late November, when routine radio contact with the spacecraft is re-established, the team will collect data to determine how closely MESSENGER followed its plans and to update knowledge of its orbit. This information will enable operators to plan for the December 12 trajectory correction maneuver that will target the spacecraft for the second Venus flyby.

The spacecraft is relying on multiple planetary flybys to "catch" Mercury and begin orbiting the planet. Another flyby of Venus in June of 2007 will further alter the spacecraft's orbit so that it will fly by Mercury in January of 2008. Three close approaches to Mercury will be required to bring the velocity of MESSENGER close enough to the orbital velocity of Mercury such that its main engine can brake the spacecraft into Mercury orbit in March of 2011.

MESSENGER, short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging, will conduct the first orbital study of Mercury, the least explored of the terrestrial ("rocky") planets that also include Venus, Earth, and Mars. Over the period of one Earth year -- four Mercury years -- MESSENGER will provide the first images of the entire planet and collect detailed information on the composition and structure of Mercury's crust, its geologic history, the nature of its atmosphere and magnetosphere, and the makeup of its core and polar materials.